Know Your Onions

The next time you do something like that I am going to knock your block off.

Knock Your Socks Off :

If something knocks your socks off, it amazes and surprises you usually in a positive way.

Know A Hawk From A Handsaw :

If someone knows a hawk from a handsaw, they are able to distinguish things and assess them.

Know Full Well :

When you know full well, you are absolutely sure that you know.

Know The Ropes :

Someone who is experienced and knows how the system works knows the ropes.

Know Where All The Bodies Are Buried :

The phrase implies that the person knowing these secrets will use that knowledge to secure something of value for himself or herself. Someone who by virtue of holding a position of trust with an organization for a long period of time has come to know many of the secrets that others in more powerful positions would rather be kept secret knows where the bodies are buried.

Know Which Side of The Bread is Buttered On :

If you know which side of the bread is buttered on, you know where your interests lie and will act accordingly to protect or further them.

Know Which Way The Wind Blows :

This means that you should know how things are developing and be prepared for the future.

Know Your Onions :

If someone is very well-informed about something, they know their onions.

Know Your Place :

A person who knows his place does not try to impose himself on others.